Stable supply of electrical power is getting more and more important for the high-tech era, and protection to business from damage caused by power failure is one of the key factors for the success of a high-tech company. Damage caused by power failure includes computer down, loss of hard disk data, and break of power facility. The consequence caused by power failure is in general very hard to remedy for business.
To cope with the problem, an automatically switchable dual-power-circuit-loop circuit system is available in the market, which has a system architecture that is connected with two power sources of different voltage output circuit loops, such as an alternating current (AC) power source provided by electric main and a direct current (DC) power source provided by an un-interrupt power supply, respectively serving as a primary power source and a backup power source. In case that the primary power source cannot supply sufficient power or the primary power source is cut off, the automatically switchable dual-power-circuit-loop circuit system automatically switches to the backup power source to continue stable supply of power in order to protect the associated facility from damage caused by the power collapse.
FIG. 1 of the attached drawings shows a circuit diagram of a conventional automatically switchable dual-power-circuit-loop circuit system, which comprises a first voltage output circuit loop 100 and a second voltage output circuit loop 200. The first voltage output circuit loop 100 is generally comprised of a rectifier circuit 11, a filter circuit 12, an output transformer 2, a pulse-width-modulation (PWM) control circuit 3, and a first voltage output rectification/regulation circuit 4.
A first power source ACV supplies an operation voltage through the rectifier circuit 11 and the filter circuit 12 to a primary-side winding 21 of the output transformer 2 and a secondary-side winding 22 of the output transformer 2 in turn generates a secondary-side output voltage, which is applied through a rectification circuit 41 and a regulation circuit 42 of the first voltage output rectification/regulation circuit 4 to thereby provide a first output voltage DCV1.
The first output voltage DCV1 is fed through a diode 43 and is then applied to a DC voltage output terminal 5. On the other hand, the first output voltage DCV1 is also applied to a feedback circuit 44 to generate a feedback signal Sfb applied to the PWM control circuit 3.
The PWM control circuit 3 is generally comprised of a PWM controller 31, a gate driving circuit 32, a transistor switching element 33, and a sensing resistor 34. The PWM control circuit 31 receives the feedback signal Sfb generated by the feedback circuit 44 and in turn generates at an output terminal thereof, based on the feedback signal Sfb, a reference voltage Vref, and a detected signal Ssen detected by the sensing resistor 34, a gate control signal Sg, which is applied to the gate driving circuit 32 to drive the operation of the transistor switching element 33 to further control the excitation of the primary-side winding 21 of the output transformer 2. The output transformer 2 further comprises a PWM operation voltage winding 23, which generates a PWM operation voltage Vdd to the PWM controller 31.
In the second voltage output circuit loop 200, a second power source 61 and a diode 62 connected in series to the second voltage output circuit loop 200 are included. The second power source 61 supplies a second output voltage DCV2, which is applicable to the DC voltage output terminal 5.
The previously described conventional circuit suffers the drawbacks of high power consumption and being easy to generate high temperatures in components thereof. It is apparent from the conventional circuit that in normal supply of electrical power, the first voltage output circuit loop 100 provides the first output voltage DCV1 to the output terminal 5, while the second voltage output circuit loop 200 is cut off; and in case that the first voltage output circuit loop 100 fails to supply electrical power, the second voltage output circuit loop 200 starts to supply the second output voltage DCV2 to the output terminal 5. Since large currents are supplied through the diodes 43, 62, great amounts of power are consumed and problems of high temperature may be caused.
Another known automatically switchable dual-power-circuit-loop circuit system adopts power control integrated circuit (IC) to replace the diodes that are used in the previously described conventional technology. In this way, improved control and removal of the drawbacks of high power consumption and high temperature are achieved, but using power controlling means (including power transistor), which is generally of high expense, to substitute the simply-structured diode circuit makes the costs of the known circuit very high.